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From: jrd@tad.eds.com (Jay Dunning)
Newsgroups: comp.std.c++
Subject: STL: A few more operations needed
Date: 27 Mar 1995 15:58:25 GMT
Organization: EDS
Lines: 48
Distribution: world
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In a comparison of STL with the Smalltalk 80 collection classes, STL
seemed to be missing the following:

for_each_if(first, last, func, pred)

	Applies func to each element in the range [first, last) for 
	which pred(*i) == true.  (This is comparable to the Smalltalk
	select method.)

multiset::insert(x, n)

	Inserts n copies of x.  (For compatibility with
	sequences and ST80 Bag class.)

{multi}map::find_value(first, last, value)

	Returns the first iterator i in the range [first, last) for
	which (*i).second == value.

const {multi}map::operator[](key) const

	Returns a reference to the value associated with key, without
	inserting a new element if key is not found.  This would 
	probably have to return a null reference for a not-found 
	condition, which may be politically incorrect, but I find
	the current behavior of operator[] counter-intuitive.  Besides,
	not having a const operator[] violates one of Scott Meyers' rules.

It would be useful to have iterator adaptors that could extract just 
the key or just the value from a {multi}map.

It might also be useful to support relational composition (like Smalltalk
MappedCollection):
	template <class MappedContainer1, class MappedContainer2>
	class composed_map {
          public:
            composed_map(MappedContainer1& mapa, MappedContainer2& mapb);
            reference operator[](const key_type& x)
                { return mapb[mapa[x]]; }
        };
(I would have preferred to show a non-template class inheriting from a base
class also common to map and multimap.)

Also, it seems to me that remove_copy() would be more appropriately called
copy_if(), since it does not actually remove elements (as does remove()), 
and it takes a predicate. This would require the behavior to be changed
from copying elements that fail the predicate to copying elements that
satisfy the predicate.